Automatic retransmission and error recovery for packet oriented point-to-multipoint communication

ABSTRACT

Point to multipoint wireless communication, including automatic retransmission and error recovery for packet oriented point to multipoint communication, which integrates adaptive and dynamic responsiveness for parameters for automatic retransmission using wireless communication. A wireless communication link is divided into a downstream portion and an upstream portion. Parameters are selected for automatic retransmission independently for the downstream portion and the upstream portion of the wireless communication link. A BSC controls the selection of parameters for automatic retransmission for all CPE within a cell. As part of a TDD frame, in which the BSC and the CPE share communication bandwidth using a TDMA technique, the BSC includes its selection of parameters for automatic retransmission to be used by CPE within a control section of the TDD frame. The BSC dynamically and adaptively determines new selected parameters for automatic retransmission, in response to conditions of a wireless communication link with each independent CPE. The BSC dynamically and adaptively allocates acknowledgement time slots within the upstream portion of the TDD frame, for use by each selected CPE. The BSC allocates some portion of the upstream bandwidth as a shared resource and some portion of the upstream bandwidth as unshared when there are messages received but not yet acknowledged. The BSC dynamically and adaptively response to acknowledgement and non-acknowledgement messages from each selected CPE, to integrate the automatic retransmission protocol with the TDD frame and the TDMA technique used within that frame.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of and hereby incorporates byreference and claims benefit of U.S. application Ser. No. 09/689,271,filed Oct. 11, 2000, now U.S. Pat. No. 6,636,488.

BACKGROUND OF THE INVENTION

A portion of the disclosure of this patent document contains materialwhich is subject to copyright protection. The copyright owner has noobjection to the facsimile reproduction by anyone of the patent documentor the patent disclosure, as it appears in the Patent and TrademarkOffice patent file or records, but otherwise reserves all copyrightrights whatsoever.

1. Field of the Invention

This invention relates to wireless communication systems, such as thoseincluding automatic retransmission and error recovery for packetoriented point-to-multipoint communication.

2. Related Art

In communication systems, messages from a sender to a receiver using acommunication link are sometimes subject to sending errors, such as biterrors, unreasonable sending delay, unintended reordering, andunintended duplication of messages. For example, noise on thecommunication link can cause bits within messages to be incorrect,generally causing the receiver to be unable to use the message. In awireless communication system, these problems are exacerbated by avariety of circumstances that are specific to wireless communication.For example, co-channel interference (CCI), multipath and multipointeffects, such as refraction or reflection resulting in intrasymbolinterference and intersymbol interference, are often prevalent withwireless communication, and can substantially reduce the reliability ofwireless communication links.

One known method in digital communication systems is to implement anautomatic retransmission protocol between sender and receiver, so thatthe receiver acknowledges messages from the sender, and the senderre-transmits those messages not acknowledged by the receiver within areasonable time. Known automatic retransmission protocols includeseveral parameters, which must generally be selected in response tocharacteristics of the communication link, to optimize communicationthroughput between the sender and receiver.

One problem with application of this known method to wirelesscommunication systems is that there are multiple physicalcharacteristics of the wireless communication link, each which isspecific to a particular combination of sender and receiver, and each ofwhich can change substantially over relatively short time durations.These multiple physical characteristics can include characteristics ofthe sender's equipment or of the receiver's equipment, characteristicsof objects on or near communication pathways between the sender and thereceiver, and characteristics of other communications overlappingcommunication between the sender and the receiver. For example, thewireless communication environment can include substantial changes inwireless communication link characteristics in the time duration betweensending a message and sending an appropriate acknowledgement for thatmessage. This is particularly so for characteristics related to errorsin sending information using wireless communication links, includinginterference such as CCI, and multipath and multipoint effects.Moreover, multiple ones of these physical characteristics can changeindependently of one another, and can have substantial and relativelyunpredictable effects on one another.

Accordingly, selection of a single set of parameters with which tooptimize automatic retransmission using a wireless communication link isvirtually always suboptimal for communication among multiple senders andmultiple receivers. Moreover, selection of parameters with which tooptimize automatic retransmission can be subject to substantial datacollection and computation; this task is not easily distributed amongmultiple senders and multiple receivers. Accordingly, it would beadvantageous to provide a technique for automatic retransmission anderror recovery for packet oriented point to multipoint communication,that is not subject to drawbacks of the known art. Preferably, in such atechnique, automatic retransmission and error recovery characteristicsare responsive to changes in the characteristics of the communicationlink between sender and receiver.

SUMMARY OF THE INVENTION

The invention provides a method and system for point to multipointwireless communication, including automatic retransmission and errorrecovery for packet oriented point to multipoint communication. Themethod and system integrates adaptive and dynamic responsiveness forparameters for automatic retransmission using wireless communication,both for single sender and a single receiver, and for sets of multiplesenders and multiple receivers.

In a first aspect of the invention, the wireless communication link isdivided into a downstream portion and an upstream portion. The methodand system selects parameters for automatic retransmission independentlyfor the downstream portion and the upstream portion of the wirelesscommunication link. A base station controller (BSC) controls theselection of parameters for automatic retransmission for all customerpremises equipment (CPE) within a cell. As part of a TDD frame, in whichthe BSC and the CPE share communication bandwidth using a TDMAtechnique, the BSC includes its selection of parameters for automaticretransmission to be used by CPE within a control section of the TDDframe.

Preferably in this aspect of the invention, the BSC dynamically andadaptively determines new selected parameters for automaticretransmission, in response to conditions of a wireless communicationlink with each independent CPE. One problem particular to this aspect ofthe invention, and overcome by the invention, is that when the BSC sendsnew selected parameters for using the wireless communication link,aspects of each message to be sent will also dynamically vary. These caninclude the size of each message (in bytes or message symbols), the timeduration for each message, and other aspects of each message.Accordingly, in the second aspect of the invention, parameters forautomatic retransmission are responsive to a number of bytessuccessfully sent from a sender to a receiver, rather than responsive toa number of messages successfully sent or a number of symbolssuccessfully sent.

In a second aspect of the invention, upstream retransmission control isplaced in the receiver of the upstream communication (i.e., the BSC)rather than the transmitter of the upstream communication (i.e., theCPE). In order to control retransmission, the BSC dynamically andadaptively allocates acknowledgement time slots within the upstreamportion of the TDD frame for use by each selected CPE. Thus, the BSC, inaddition to determining parameters for automatic retransmission, alsodetermines an amount of bandwidth allocated to each selected CPE forsending messages associated with automatic retransmission (such asacknowledgement or non-acknowledgement messages). As part of this secondaspect of the invention, the BSC allocates some portion of the upstreambandwidth as a shared resource and some portion of the upstreambandwidth as unshared (that is, specifically allocated to a selectedCPE) when there are messages received but not vet acknowledged.

In a third aspect of the invention, the BSC dynamically and adaptivelyresponds to acknowledgement and non-acknowledgement messages from eachselected CPE, to integrate the automatic retransmission protocol withthe TDD frame and the TDMA technique used within that frame. In apreferred embodiment, when the BSC sends messages to a selected CPE, theBSC sets a first timeout each time it receives a non-acknowledgementmessage from that selected CPE; during this first timeout duration, theBSC discards further acknowledgement and non-acknowledgement messagesfrom that selected CPE. Also in a preferred embodiment, when the BSCreceives messages from a selected CPE, the BSC sets a second timeouteach time it receives an invalid message from the selected CPE; duringthis second timeout duration, the BSC discards all further messagesreceived from that selected CPE.

The invention provides an enabling technology for a wide variety ofapplications for communication, so as to obtain substantial advantagesand capabilities that are novel and non-obvious in view of the knownart. Examples described below primarily relate to wireless communicationsystems, but the invention is broadly applicable to many different typesof communication in which characteristics of the communication link aresubject to change.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of a portion of a system using automaticretransmission and error recovery in a point to multipoint wirelesscommunication.

FIG. 2 shows a time division duplex frame used in a system as in FIG. 1.

FIG. 3 shows a process flow diagram of a method for operating a systemas in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the following description, a preferred embodiment of the invention isdescribed with regard to preferred process steps and data structures.Embodiments of the invention can be implemented using general-purposeprocessors or special purpose processors operating under programcontrol, or other circuits, adapted to particular process steps and datastructures described herein. Implementation of the process steps anddata structures described herein would not require undue experimentationor further invention.

RELATED APPLICATIONS

Inventions described herein can be used in conjunction with inventionsdescribed in the following documents.

-   -   U.S. patent application Ser. No. 09/475,642, Express Mail        Mailing No. EL524780018US, filed Dec. 30, 1999 in the names of        Reza Majidi-Ahy, Subir Varma, Khuong Ngo, Jean Fuentes and Paul        Truong, now U.S. Pat. No. 6,650,623, titled “Adaptive Link Layer        for Point to Multipoint Communication System.”    -   U.S. patent application Ser. No. 09/475,716, Express Mail        Mailing No. EL524780021US, filed Dec. 30, 1999 in the names of        Reza Majidi-Ahy, Joseph Hakim, and Subir Varma, now U.S. Pat.        No. 6,654,384, titled “Integrated Self-Optimizing        Multi-Parameter and Multi-Variable Point to Multipoint        Communication System.”    -   U.S. patent application Ser. No. 09/540,674, Express Mail        Mailing No. EL524781512US, filed Mar. 31, 2000, in the name of        Reza Majidi-Ahy, attorney docket number 164.1001.01, titled        “Robust Topology Wireless Communication Using Broadband Access        Points.”    -   U.S. patent application Ser. No. 09/604,784, Express Mail        Mailing No. EL524781225US, filed Jun. 26, 2000 in the names of        Reza Majidi-Ahy, attorney docket number 164.1010.01, titled        “High-Capacity Scalable Integrated Wireless Backhaul for        Broadband Access Networks.” and    -   U.S. patent application Ser. No. 09/620,826, Express Mail        Mailing No. EL524780959US, filed Jul. 21, 2000 in the name of        Reza Majidi-Ahy, Joseph Hakim, and Subir Varma, titled        “Integrated, Self-Optimizing, Multi-Parameter/Multi-Variable        Point-to-Multipoint Communication System [II].”

Each of these documents is hereby incorporated by reference as if fullyset forth herein. This application claims priority of each of thesedocuments. These documents are collectively referred to as the“Incorporated Disclosures.”

Lexicography

The following terms refer or relate to aspects of the invention asdescribed below. The descriptions of general meanings of these terms arenot intended to be limiting, only illustrative.

-   -   base station controller (BSC)—in general, a device for        performing coordination and control for a wireless communication        cell. There is no particular requirement that the base station        controller must be a single device; in alternative embodiments,        the base station controller can include a portion of a single        device, a combination of multiple devices, or some hybrid        thereof.    -   communication link—in general, an element for sending        information from a sender to a recipient. Although in a        preferred embodiment the communication links referred to are        generally wireless line of sight point to point communication        links, there is no particular requirement that they are so        restricted.    -   customer premises equipment (CPE)—in general, a device for        performing communication processes and tasks at a customer        location, and operating in conjunction with the base station        controller within a wireless communication cell. There is no        particular requirement that the customer premises equipment must        be a single device; in alternative embodiments, the customer        premises equipment can include a portion of a single device, a        combination of multiple devices, or some hybrid thereof.    -   IP parameters—in general, a set of characteristics or parameters        relating to an IP layer for a communication link.    -   media-access-control (MAC) parameters—in general, with reference        to a wireless communication link, a set of characteristics or        parameters relating to media access control of a communication        link. For example, MAC parameters can include (a) a number of        payload data bytes assigned per message, (b) a frequency of        acknowledgement messages and a number of message retransmission        attempts, (c) a fraction of the communication link allocated to        downstream versus upstream communication, and the like.    -   physical (PHY) parameters—in general, with reference to a        wireless communication link, a set of characteristics or        parameters relating to physical transmission of information on a        communication link. For example, physical characteristics can        include (a) a symbol transmission rate, (b) a number of payload        data bits assigned per symbol, (c) a number of error detection        or correction bits assigned per symbol, and the like.    -   QoS parameters—in general, a set of characteristics or        parameters relating to QoS (quality of service) for a        communication link.    -   wireless communication system—in general, a communication system        including at least one communication link that uses wireless        communication techniques.    -   wireless transport layer—in general, a set of protocols and        protocol parameters for sending and receiving information using        wireless transport. In a preferred embodiment, the wireless        transport layer is part of a multilayer systems architecture, in        which the wireless transport layer is built using a physical        transport layer, and the wireless transport layer is used by a        logical transport layer such as IP.

As noted above, these descriptions of general meanings of these termsare not intended to be limiting, only illustrative. Other and furtherapplications of the invention, including extensions of these terms andconcepts, would be clear to those of ordinary skill in the art afterperusing this application. These other and further applications are partof the scope and spirit of the invention, and would be clear to those ofordinary skill in the art, without further invention or undueexperimentation.

System Context

The context of the invention is similar to that of the IncorporatedDisclosures.

A system using adaptive point to multipoint wireless communication in awireless communication system operates as part of a system in whichdevices coupled to a network (such as a computer network) send messages,route and switch messages, and receive messages. In a preferredembodiment, devices coupled to (and integrated with) the network send,route, and receive these messages as sequences of packets, each of whichhas a header including delivery information and a payload includingdata. In a preferred embodiment, packet format conforms to the OSImodel, in which an application protocol (layer 5, such as FTP), uses atransport protocol (layer 4, such as TCP), which uses a network protocol(layer 3, such as IP), which uses a media access control (MAC) protocol(layer 2), which uses a physical transport technique (layer 1).

The system using adaptive point to multipoint wireless communication isdescribed herein with regard to layer 1 and layer 2, particularly as itapplies to interactions between layer 1 and layer 2 and between thoselayers and layer 3. However, concepts and techniques of the inventionare also applicable to other layers of the OSI model. The applicationgives examples of cases where the type of application in the applicationlayer (layer 5) could be incorporated into embodiments of the inventionto improve communication. Adapting those concepts and techniques to suchother layers would not require undue experimentation or furtherinvention, and is within the scope and spirit of the invention.

System Elements

FIG. 1 shows a block diagram of a portion of a system using automaticretransmission and error recovery in a point to multipoint wirelesscommunication.

A system 100 includes a wireless communication cell 110 (or a portionthereof), a base station controller (BSC) 120, one or more customerpremises equipment (CPE) 130, and one or more (possibly partially)interfering or reflecting obstacles 140.

The wireless communication cell 110 includes a generally hexagon-shapedregion of local surface area, such as might be found in a metropolitanregion. Use of generally hexagon-shaped regions is known in the art ofwireless communication because they are able to tile a local region withsubstantially no gaps. However, although in a preferred embodiment thewireless communication cell 110 includes a generally hexagon-shapedregion, there is no particular requirement for using that particularshape; in alternative embodiments it may be useful to provide anothershape or tiling of the local surface area.

In FIG. 1, a portion of the cell 110, herein called a “sector” 111,includes a generally triangular-shaped region of local surface area,disposed so that a set of six sectors 111 are combined to form a singlecell 110. Thus, the BSC 120 is disposed at or near one corner of thesector 111, while CPE 130 are disposed within the sector 111. Moreover,obstacles 140 are disposed within the sector 111 or at junctions ofmultiple sectors 111.

Although the invention is primarily described with regard to a singlesector 111, there are substantial applications of the invention tointeraction between multiple sectors 111 within a cell 110, and tointeraction between sectors 111 in multiple cells 110. These substantialapplications of the invention are described at least in part in thisapplication. Moreover, other and further substantial applications of theinvention with regard to multiple sectors 111, both within a single cell110 and among multiple cells 110, would be clear to those skilled in theart of wireless communication after perusal of this application, andwould not require undue experimentation or further invention.

The BSC 120 includes a processor, program and data memory, mass storage,and one or more antennas for sending or receiving information usingwireless communication techniques.

Similar to the BSC 120, each CPE 130 includes a processor, program anddata memory, mass storage, and one or more antennas for sending orreceiving information using wireless communication techniques.

Obstacles 140 might include buildings, other construction,electromagnetically active elements such as radio transmitters andrepeaters, other electromagnetic elements such as power lines or weathereffects, and possibly mobile objects such as vehicles.

Although the invention is primarily described with regard to non-movingobstacles 140, it would be clear to those of ordinary skill in the artof wireless communication, after perusal of this application, that evennon-moving obstacles 140 might present substantial variation over timein characteristics of communication links between the BSC 120 andselected CPE 130. Moreover, there are substantial applications of theinvention to cells 110 and sectors 111 in which there are movingobstacles 140. Although these substantial applications of the inventionare not described in great detail herein, other and further substantialapplications of the invention with regard to moving obstacles 140, bothwithin a single cell 110 and among multiple cells 110, would be clear tothose skilled in the art of wireless communication after perusal of thisapplication, and would not require undue experimentation or furtherinvention.

Communication among devices within the wireless communication cell 110is preferably conducted on a one-to-one basis between each CPE 130 andthe BSC 120. Thus, the BSC 120 communicates with each CPE 130, and eachCPE 130 communicates with the BSC 120. In a preferred embodiment, CPE130 do not communicate directly with other CPE 130. However, inalternative embodiments, CPE 130 may communicate directly with other CPE130, with the characteristics of such communication being controlledeither by the BSC 120, by one CPE 130 selected by the BSC 120, or by oneCPE 130 mutually agreed to among the communicating CPE 130.

Communication between the BSC 120 and each CPE 130 is conducted using aTDD technique, in which time durations are divided into repeatedindividual frames, each one of which includes a “downstream” portion andan “upstream” portion. Unlike existing protocols in which transmissionsare controlled by the transmitting side, the BSC 120 controlstransmissions for both upstream and downstream directions, withoutspecific requests from CPE 130.

Time Division Duplex (TDD) Frame

FIG. 2 shows a time division duplex frame used in a system as in FIG. 1.

During the downstream portion of each frame, the BSC 120 transmits, thussending information to one or more CPE 130. During the upstream portionof each frame, each CPE 130 is potentially allocated a time slot fortransmission, thus for sending information to the BSC 120. TDDtechniques are known in the art of wireless communication.

A time division duplex (TDD) frame 200 includes a time-synchronizationportion 210, a first guard time 220, a downstream portion 230, a secondguard time 240, a status-synchronization portion 250, and an upstreamportion 260.

The time-synchronization portion 210 includes a first symbol 211indicating the beginning of the TDD frame 200, and a sequence ofparameter setting values 212 for each CPE 130. The BSC 120 uses theparameter setting values 212 to inform each selected CPE 130individually and separately of (a) the PHY and MAC parameters the BSC120 is using to send messages to that selected CPE 130, and (b) the PHYand MAC parameters the selected CPE 130 should use to send messages tothe BSC 120 during its allocated part of the upstream portion 260.

The first guard time 220 includes a time duration sufficient for the BSC120 to assure that all CPE 130 do not interfere with each other whenreceiving from the BSC 120 or sending to the BSC 120.

The downstream portion 230 includes a sequence of downstream payloadelements 231, each sent by the BSC 120 to a selected CPE 130. The BSC120 determines a length for each of these downstream payload elements231 and sends that information with the parameter setting values 212 inthe time-synchronization portion 210. In alternative embodiments, theBSC 120 may divide the CPE 130 into classes and allocate one or moredownstream payload elements 231 for each class of CPE 130. For example,the BSC 120 may allocate one or more downstream payload elements 231 forbroadcast or multicast messages.

The second guard time 240 includes a time duration sufficient for theBSC 120 to assure that the downstream portion 230 and thestatus-synchronization portion 250 do not interfere.

The status-synchronization portion 250 includes a sequence of statusinformation so that the BSC 120 can agree with each selected CPE 130regarding higher-level protocol status out-of-band from thosehigher-level protocols.

Similar to the downstream portion, the upstream portion 260 includes asequence of upstream payload elements 261, each sent by a selected CPE130 to the BSC 120. The BSC 1120 (not the CPE 130) determines a lengthfor each of these upstream payload elements 261 and sends thatinformation with the parameter setting values 212 in thetime-synchronization portion 210. In alternative embodiments, the BSC120 may divide the CPE 130 into classes and allocate one or moreupstream payload elements 261 for each class of CPE 130, such as forupstream bandwidth contention.

Method of Operation

FIG. 3 shows a flow diagram of a method for operating a system as inFIG. 1.

A method 300 includes a set of flow points and a set of steps. Thesystem 100 performs the method 300. Although the method 300 is describedserially, the steps of the method 300 can be performed by separateelements in conjunction or in parallel, whether asynchronously, in apipelined manner, or otherwise. There is no particular requirement thatthe method 300 be performed in the same order in which this descriptionlists the steps, except where so indicated.

At a flow point 310, the BSC 120 and the CPE 130 are ready to begin aTDD frame.

At a step 311, the BSC 120 and the CPE 130 conduct communication using aTDD frame. As part of this step, the BSC 120 directs the CPE 130regarding which physical parameters and MAC parameters to use.

At a step 312, the BSC 120 determines characteristics of thecommunication link with the CPE 130, in response to performance of thecommunication during the previous TDD frame.

At a step 313, the BSC 120 determines exact values for the physicalparameters and MAC parameters in response to characteristics of thecommunication link.

At a step 314, the BSC 120 determines new values for the physicalparameters and MAC parameters for automatic retransmission in responseto results of the previous step.

The BSC 120 preferably determines these automatic retransmissionparameters dynamically and adaptively for all CPEs 130 in cell 110. Theautomatic retransmission parameters preferably are determinedindependently for each upstream portion and each downstream portion andindependently for each CPE.

In order to account for differing characteristics of transmission andretransmission among the CPEs (e.g., message size and duration, symbolsize, and other aspects), parameters for retransmission preferably areresponsive to a number of bytes successfully transmitted rather than anumber of messages or symbols successfully transmitted.

At step 315, the BSC 120 dynamically and adaptively allocatesacknowledgement time slots within upstream portion 260 of each TDD framefor use by the CPEs 130. As part of this step, the BSC 120 preferablyallocates some portion of the upstream bandwidth as a shared resourceand some portion of the upstream bandwidth as unshared (that is,specifically allocated to selected CPEs) when there are messagesreceived but not yet acknowledged.

Thus, control of upstream retransmission is placed within the BSC, notthe CPE. This control allows the BSC 120 to distribute acknowledgementslots for plural CPEs across plural TDD frames, thereby allowing the BSC120 to prevent the acknowledgement slots from consuming too muchbandwidth.

At step S316, the BSC 120 dynamically and adaptively responds toacknowledgement and non-acknowledgement messages from each selected CPE130 so as to integrate the automatic retransmission protocol with theTDD frame and the TDMA technique used within that frame.

In the preferred embodiment, when the BSC 120 sends messages to aselected CPE 130, the BSC 120 sets a first timeout each time the BSC 120receives a non-acknowledgement message from that selected CPE. Duringthis first timeout duration, the BSC 120 discards furtheracknowledgement and non-acknowledgement messages from that selected CPE130.

Also in the preferred embodiment, when the BSC 120 receives messagesfrom a selected CPE 130, the BSC 120 sets a second timeout each time itreceives an invalid message from the selected CPE 130. During thissecond timeout duration, the BSC 120 discards all further messagesreceived from that selected CPE 130.

After step 316, the BSC 120 and the CPE 130 have performed one step ofsending and receiving information using a TDD frame. The flow point 310is reached repeatedly and the steps thereafter are performed repeatedly,for each TDD frame.

Pseudo-code for implementing the preferred embodiment of the inventionsubstantially as discussed above is included in a technical appendix tothis application.

Generality of the Invention

The invention has general applicability to various fields of use, notnecessarily related to the services described above. For example, thesefields of use can include one or more of, or some combination of, thefollowing:

-   -   The invention is applicable to other forms of wireless        communication, such as frequency division multiple access (FDMA)        or code division multiple access (CDMA, also known as spread        spectrum communication);    -   The invention is applicable to any non-wireless communication,        in which relative effectiveness or efficiency of communication        can be achieved from dynamically adjusting communication        parameters, such as physical parameters or MAC parameters. For        example, the invention can be generalized to non-wireless        communication using modems in which equalization parameters are        to be dynamically adjusted.    -   The invention is applicable to other wireless communication        systems, such as satellite communication systems and (microwave        tower or other) point to point transmission systems.    -   The invention is applicable to both fixed wireless communication        systems, in which customer premises equipment do not move        relative to the BSC 120, and to mobile wireless communication        systems, and which customer premises equipment move        substantially relative to the BSC 120.    -   The invention is applicable to both a single sender and a single        receiver, and sets of multiple senders and multiple receivers.

Other and further applications of the invention in its most generalform, will be clear to those skilled in the art after perusal of thisapplication, and are within the scope and spirit of the invention.

Although preferred embodiments are disclosed herein, many variations arepossible which remain within the concept, scope, and spirit of theinvention, and these variations would become clear to those skilled inthe art after perusal of this application.

TECHNICAL APPENDIX Pseudo-code copyright 2000 Aperto Networks, Inc. 4.0Downstream ARQ (BSC Tx, CPE Rx) 4.1 Parameters (Control PDU Handler)  ARQWindowSize; // Size of the ARQ window. Set to 2{circumflex over( )}(n−1) bytes, where n is the // number of bits in the Sequence Numberfield   maxAcksLost; // Maximum number retries for the upstream ACKs,after which // the CPE is re-ranged   maxReqRetries; // Maximum numberof retries for a REQ packet. 4.2 BSC Tx (reqWin, scWin, curWin, ackWin)4.2.1 Initialize (Control PDU Handler)   reqWinOff = 0; // Sequencenumber of next byte to be queued   scWinOff = 0; // Sequence number ofnext byte to be transmitted by BSC   curWinOff = 0; // Sequence numberof next byte the CPE expects   ackWinOff = 0; // Sequence Number of nextbyte awaiting acknowledgment // Allocate empty SIDQ_EL and initializepointers   newSidQEl = AllocateSidQEl( );   newSidQEl->EOL = TRUE;  writeElPtr = ackElPtr = curElPtr = scElPtr = newSidQEl;   ackPtr =curPtr = scPtr = 0;   retryCnt = 0; // Used to decide when to drop apacket   NumAcksLost = 0; // Used for link adaptation 4.2.2 PDU Arrival(Classifier, Policer)   // Classify the WPDU     find sidQ (PDU); //Classifier   // Enqueue the WPDU on the overflow section of the sidQ    newSidQEl = AllocateSidQEl( ); // Policer     newSidQEl->EOL = TRUE;// Policer     writeElPtr->next = newSidQEl; // Policer    writeElPtr->length = PDU.length; // Policer     writeElptr->txMsgPtr= PDU.txMsgPtr; // Policer     writeElPtr->pktPtr = PDU.packet; //Policer     writeElPtr = newSidQEl; // Policer   // Traffic shaping maybe done before the packet is moved out of the overflow section.   //These updates must be done last to avoid timing problems with USG.    reqWinOff = reqWinOff + PDU.size; // Policer     writeElPtr->EOL =FALSE; // Policer 4.2.3 MAP Construction (Scheduler)   while (space leftfor data in downstream TDD frame) {     sidQCtrl = SID that Schedulerselects;     bytesInQueueToSchedule = reqWinOff − scWinOff;     //Always try to schedule bytes for SIDs without ARQ.     // For SIDs withARQ, we need to make sure that we have not     // exhausted our windowbefore we try to schedule some bytes.     if ( (sidQCtrl.sidCfgBits.arq= FALSE) OR       ((scWinOff + bytesScheduled − ackWinOff) <ARQWindowSize) ) {       DATA_GRANT_IE.winOff = scWinOff;      DATA_GRANT_IE.payloadSize = bytesScheduled; // Includes delimiter  bytes       scWinOff = scWinOff + DATA_GRANT_IE.payloadSize;      allocate ticks for WPDU in downstream portion of TDD Frame;      update scElPtr and scPtr to reflect bytes scheduled;       // MarkSID as needing ACK       if ( (sidQCtrl.sidCfgBits.ack = TRUE) AND(!sidQCtrl.ackFlag) ) {         sidQCtrl.ackFlag = TRUE;         add tolist of downstream SIDs needing ACK; } } } // while (space   left)   //Schedule only one ACK per SID for a frame.   // We can schedule ACKs forSIDs without ARQ. This is needed for link adaptation.   for each SID onlist of downstream SIDs needing ACK {     // If there are bytesremaining to be acked, allocate space for the     // ACK even if thecurrent frame has no WPDUs scheduled for this SID     if (scWinOff !=ackWinOff) {       Allocate ticks for ACK in the upstream portion of TDDframe;       ACK_IE.sid = this SID; }   else {     delete from list ofSIDs needing ACK;     sidQCtrl.ackFlag = FALSE; }   } // for (each SIDon list) 4.2.4 MAP Arrival (Hardware)   if (data grant IE) {     // Wasa packet dropped or retransmitted?     if((sidQCtrl.sidCfgBits.arq =TRUE) AND     (curWinOff!=DATA_GRANT_IE.winOff)){       // if possible,check (ackWinOff == DATA_GRANT_IE.winOff)       curWinOff = ackWinOff;      Reset the cur pointers to the ack pointers; }     // Needpseudocode for HW packet fragmentation     Build a WPDU using thecurElPtr and curPtr     WPDU.winOff = curWinOff; // Should we use datagrant ie not curWin?? JF     curWinOff = curWinOff +DATA_GRANT_IE.payload     Update curElPtr and curPtr to reflect bytestransmitted } 4.2.5 WPDU Transmit (Hardware)   transmit built WPDU;   if(sidQCtrl.sidCfgBits.arq == FALSE)     return any completely transmittedpacket; 4.2.6 ACK Arrival (Scheduler)   // Calculate the number of ACKedbytes   NumAcksLost = 0;   ackByteCnt = ACK.winOff − ackWinOff;   //Only free buffers here if ARQ. Otherwise they'd have been freed rightafter transmit.   if (sidQCtrl.sidCfgBits.arq == TRUE) {     // Anybytes ACKed?     if (ackByteCnt) {       ackWinOff = ackWinOff +ackByteCnt;       tempElPtr = ackElPtr;       update ackPtr and ackElPtrto account for the bytes ACKed;       if (tempElPtr != ackElPtr)        free SIDQ_ELs between ackElPtr and tempElPtr;       if(ACK.nakFlag clear)         retryCnt = 0; }     // Any bytes NACKed?    if (ACK.nakFlag set) {       if ((ackByteCnt == 0) && (time >threshold)) {         threshold = time at which the last (partially)allocated TDD frame           ends;         retryCnt = retryCnt + 1; }      // When the retry count expires, drop only the first packet in thelist.       if (retryCnt > sidQCtrl.maxRetry) {         // pktPtr pointsto the first byte in the packet, and ackPtr is the off-   set         //from pktPtr to the next byte to ack         dropBytes = ackElPtr->length− ackPtr;         tempElPtr = ackElPtr;         update ackElPtr to nextpacket in list;         ackPtr = 0;         free (tempElPtr);         //Account for any bytes that need to be retransmitted         reqWinOff −=dropBytes; // Scheduler asks Policer to do this and   does // notschedule any more bytes for this SID // until it is done.         informlink adaptation task that we dropped an EPDU }       // We have toreschedule some bytes for retransmission       scWinOff = ackWinOff;      update sc pointers to ack pointers;     } // if nakByteCnt   } //if ARQ 4.2.7 ACK Lost (Scheduler)   NumAcksLost = NumAcksLost + 1;   if(NumAcksLost > maxAcksLost)     ReRange CPE;   // Note: ACK may be lostif the corresponding MAP was lost. However it is not clear how   // alost MAP event may be detected by the BSC.   // Note: If a CPE cannot beReRanged, the Link Adaptation Task needs to send a message   // to theControl PDU Handler to flush the sidQ. 4.3 CPE Rx (curWin) 4.3.1Initialize (Control PDU Handler)   // CPE S/W does not care aboutwinOffs   curWinOff = 0; // Sequence number of the next WPDU totransmit/receive   cur pointers = NULL; 4.3.2 WPDU Arrival (Hardware)  // Never keep bad wpdus   if (crc error) {     Set NAK flag;    Discard(WPDU);     discard any packet currently being reassembled; }  else if (no energy detected)     Set NAK flag;   // If an out ofsequence wpdu arrives and this SID has ARQ, discard the   // wpdu untilwe receive the next sequence number we are expecting.   else if ((sidQCtrl.sidCfgBits.arq = TRUE) AND (WPDU.winOff != curWinOff) )    Discard(WPDU);   // Receive the WPDU. Either it's in correctsequence, or the SID has no ARQ and   // doesn't care about thesequence.   else {     curWinOff = WPDU.winOff + WPDU.payloadSize;    // Need pseudocode for HW packet reassembly     // if a new packetarrives and we were previously assembling a packet,     // we discardthe old packet and accept the new.     if ((WPDU.catPtr == 0) and(curPtr != 0)) {       Discard(Partial assembled packet);       curPtr =0;       curElPtr = NULL; }     // if possible, check the new packet forincorrect length, cuz if it's wrong, and     // we don't find it here,it'll be a real bugger to track down     if (curElPtr.length !=curPtr??)       discard packet; } 4.3.3 ACK Transmission (Hardware)   //When wpdus are scheduled for SIDs with ACK, the Scheduler   // willcreate an IE in the same MAP or in the following MAP   // for the ACK.  if (sidQCtrl.sidCfgBits.ack == TRUE) {     ACK.status = ACK or NAK;    ACK.winOff = curWinOff;     ACK.linkParms = modemStatus;    Transmit ACK; } 5.0 Upstream ARQ (CPE Tx, BSC Rx) 5.1 CPE Tx(reqWin, curWin, ackWin) 5.1.1 Initialize (Control PDU Handler)  reqWinOff = 0; // Sequence Number for the number of the next byteawaiting   // transmission.   curWinOff = 0; // Sequence Number of thenext byte that the CPE expects to tx. The   // sequence number in theMAP may be less than this, in case of   // re-transmissions.   ackWinOff= 0; // Sequence Number of the next byte awaiting acknowledgment.   //Allocate empty SIDQ_EL and initialize pointers   newSidQEl =AllocateSidQEl( );   newSidQEl->EOL = TRUE;   writeElPtr = ackElPtr =curElPtr = readElPtr = newSidQEl;   ackPtr = curPtr = 0; 5.1.2 PDUArrival (Classifier, Policer)   // Classify the WPDU   find sidQCtrl(PDU); // Classifier   // Create new empty SidQEl to terminate list  newSidQEl = AllocateSidQEl( ); // Policer   newSidQEl->EOL = TRUE; //Policer   // Enqueue the WPDU on the overflow section of the sidQ. EOLbit should already be set.   writeElPtr->next = newSidQEl; // Policer  writeElPtr->length = PDU.length; // Policer   writeElptr->txMsgPtr =PDU.txMsgPtr; // Policer   writeElPtr->pktPtr = PDU.packet; // Policer  writeElPtr = newSidQEl; // Policer   if (sidQCtrl->flushFlag not set){     wait till activeFlowFifo has room;     activeFlowFifo =PDU.sidNumber; // Policer notifies Hw }   // Traffic shaping may be donebefore the packet is moved out of the overflow section   reqWinOff =reqWinOff + PDU.size; // Policer   writeElPtr->EOL = FALSE; // Policer5.1.3 REQ Transmission (HW)   if (state = Idle) {     PDU arrival    Compute Defer     state = Deferring; }   else if (state = Deferring){     map arrives with req IE opportunity       REQ.winOff = curWinOff;      REQ.reqWinOff = reqWinOff;       Tx REQ;       state =GrantPending;   else if (state = GrantPending)     // The BSC receivedour REQ packet     map arrives with upstream data IE   transmit WPDU;  // Any more bytes left in SID queue?   if (reqWin − curWin)     state= GrantPending;   // SID queue is empty   else {     numReqRetries = 0;    state = Idle; }   // Our REQ packet did not get to the BSC   maparrives with no grant IE or grant pending IE     numReqRetries =numReqRetries + 1;     if (numReqRetries > maxReqRetries) {       HWwrites SID num plus flush flag in fifo;       HW does not tx anymorepdus until sw writes to ACTIVE_SID_FIFO;       HW setssidQCtrl->flushFlag;       numReqRetries = 0;       state = Idle; }    else       state = Deferring; 5.1.4 MAP Arrival (Hardware)   if (MAPmissing) {     calculate time of next MAP;     assume largest MAP size;    program Broadcom to receive next MAP; }   if (Data Grant IE) {    // If ARQ, don't do anything until a grant gives us the expectedoffset     if((sidQCtrl.sidCfgBits.arq == FALSE) OR      (DATA_GRANT_IE.winOff==curWinOff)){       WPDU.payloadSize =DATA_GRANT_IE.payloadSize;       Confirm that allocated ticks aresufficient to accommodate WPDU;       WPDU.req = reqWinOff;      WPDU.winOff = curWinOff; } }   if ((MAP ACK IE) OR (MAP NAK IE)) {    if (sidQCtrl.sidCfgBits.arq == TRUE) {       ackByteCnt = ACK.winOff− ackWinOff;       ackWinOff = ACK.winOff;       // Any bytes ACKed?      if (ackByteCnt) {         update ackElPtr to account for theackByteCnt;         ackPtr = 0; }       if (MAP NAK IE) {         resetcur pointers and winOff to ack pointers and winOff; }       // Notify SWof ACK, so it can free buffers.       write SID number and set ACK flagin the WM_TX_PKT_FIFO; } // if   ARQ   } // if ACK or NAK IE   if (MAPFLUSH IE) {     // The Scheduler decided it was time to give up on thepacket, so drop the     // EOL or End Of List packet.     write SIDnumber and set flush flag in WM_TX_PKT_FIFO;     setsidQCtrl->flushFlag;     // Force data transmission on this SID to halt.This gives us time to     // update the reqWinOff.     HW does not txanymore pdus until SW writes to ACTIVE_SID_FIFO;     go to req stateIdle; } 5.1.5 Process Tx Pkt Fifo (WMAC Driver)   read SID number fromWM_TX_PKT_FIFO;   if (ACK flag) {     free SIDQ_ELs from readElPtr toackElPtr;     readElPtr = ackElPtr; }   if (flush flag)     send Flushmsg to Policer; 5.1.6 Flush Packet (Policer)   // Software temporarilyhas write access to all sidQCtrl fields.   drop EOL PDU;   updateackElPtr to skip remainder of dropped PDU;   ackPtr = 0;   curWinOff =ackWinOff;   reqWinOff = reqWinOff − remainder of dropped PDU;   updatecurPtr and curElPtr to ackPtr and ackElPtr;   clear sidQCtrl->flushFlag;  // Kick off another REQ if there are any bytes still on the queue.  if (req WinOff − curWinOff)     write SID number to ACTIVE_SID_FIFO;5.1.7 WPDU Transmission (Hardware)   extract WPDU.payloadSize bytes fromposition curWinOff in SID queue;   advance curElPtr and curPtr byWPDU.payloadSize bytes;   curWinOff = curWinOff + WPDU.payloadSize;   if(sidQCtrl.sidCfgBits.arq == FALSE)     return any completely transmittedpacket; 5.2 BSC Rx (reqWin, scWin, curWin) 5.2.1 Initialize (Control PDUHandler)   scWinOff = 0; // Sequence Number of next byte to betransmitted by CPE   curWinOff = 0; // Sequence Number of the next bytethat the BSC expects   reqWinOff = 0; // Cumulative count of number ofbytes received at CPE   retryCnt = 0; // Number of times we have sentthe packet unsuccessfully. 5.2.2 REQ Arrival (Scheduler, Hardware)   if(sidQCtrl.sidCfgBits.arq == FALSE) {     scWinOff = REQ.winOff; //Scheduler     reqWinOff = REQ.reqWinOff; // Scheduler } 5.2.3 MAPConstruction (Scheduler)   // Clear ErrorRecovery state for each newframe   state = normal;   while (Space left in current Upstream TDDframe) {     sidQCtrl = SID that Scheduler selects;    bytesInQueueToSchedule = reqWinOff − scWinOff;     // Always try toschedule bytes for SIDs without ARQ.     // For SIDs with ARQ, we needto make sure that we have not     // exhausted our window before we tryto schedule some bytes.     if ( (sidQCtrl.sidCfgBits.arq == FALSE) OR      ((scWinOff + BytesScheduled − curWinOff) < ARQWindowSize) ) {      Allocate ticks for WPDU in upstream portion of TDD frame;      DATA_GRANT_IE.payloadSize = BytesScheduled;      DATA_GRANT_IE.winOff = scWinOff;       scWinOff = scWinOff +DATA_GRANT_IE.payloadSize; } } 5.2.4 WPDU Arrival (Hardware)   //Discard any bad wpdus   if (CRC Error) {     discard(WPDU);     discardany packet currently being reassembled; }   // If ARQ, discard any outof sequence wpdus   else if(sidQCtrl.sidCfgBits.arq == TRUE) AND(WPDU.winOff != curWinOff) ) {     Discard(WPDU);     Hw writes burststatus to Fifo;     send bad or dropped status to Scheduler; }   // Goodwpdu   else {     curWinOff = WPDU.winOff + WPDU.payloadSize;     //Discard packet cases -     // if a new packet arrives and we werepreviously assembling a packet     // if the packet arrives with anincorrect length     if ((WPDU.catPtr == 0) and (curPtr !=curElPtr.pktPtr)) {       Discard(Partial assembled packet);      curPtr = 0;       curElPtr = NULL; }     // if possible, check thenew packet for incorrect length     if (curElPtr.length != (curPktPtr −curElPtr.pktPtr))       discard packet;     send good status toScheduler; } 5.2.5 WPDU Status Arrives (Scheduler)   if (wpdu good) AND((sidQCtrl.sidCfgBits.arq == FALSE) OR     (ackWinOff == WPDU.winOff)) {    retryCnt = 0;     reqWinOff = WPDU.reqWinOff;     ackWinOff =WPDU.winOff + WPDU.length;     // WMAC Driver needs to calculate thisand send the new winOff to the Scheduler     if (sidQCtrl.sidCfgBits.arq== FALSE)       scWinOff = WPDU.winOff + WPDU.length; }   else if (((wpdu lost) OR (wpdu bad)) AND (sidQCtrl.sidCfgBits.arq == TRUE) ) {    // By checking the state for ErrorRecovery, this means that we just    // reset the Scheduler's window for the first bad WPDU in the frame.    // The state is reset to normal during upstream map construction.    // If a MAP is lost, then the wpdus will be lost.     if ( (time >ErrorRecoveryTime) AND (retryCnt <= sidQCtrl.maxRetry) ) {       nakFlag= TRUE;       ErrorRecoveryTime = Tick Count at end of last scheduledupstream frame;       scWinOff = curWinOff;       // Should ackWinOff =curWinOff? Verify.       update sc pointers to cur pointers;      retryCnt = retryCnt + 1; } } 5.2.6 Flush Packet (Scheduler,Policer)   // When the retry count expires, drop the packet beingassembled.   if (retryCnt > maxRetry) // Scheduler {     // When apacket is dropped, the CPE must make a new request.     scWinOff =curWinOff; // Scheduler     Update sc pointers to cur pointers; //Scheduler     retryCnt = 0; // Scheduler     flushFlag = 1; // Scheduler    Send msg to Link Adaptation Routine; // Scheduler     send msg toPolicer with sidNum; // Scheduler     reqWinOff = curWinOff; } 5.2.7Build MAP ACK IE Types (Scheduler)   if (sidQCtrl.sidCfgBits.arq ==TRUE) {     if (nakFlag) {       NACK.sidNumber = sid;       NACK.winOff= curWinOff;       Put NACK in MAP;       nakflag = FALSE; }     else if(flushFlag) {       FLUSH.sidNumber = sid;       FLUSH.winOff =curWinOff;       Put FLUSH in MAP;       flushflag = 0; }     else {      ACK.sidNumber = sid;       ACK.winOff = ackWinOff;       Put ACKin MAP; } }

1. A method of controlling selection of parameters for automaticretransmission in a point-to-multipoint wireless communication linkhaving an upstream portion for communicating data from a plurality ofcustomer premises equipment (CPE) to a base station controller (BSC) anda downstream portion for communicating data from the base stationcontroller to the plurality of customer premises equipment, the methodcomprising the steps of: selecting physical and media access control(MAC) parameters for automatic retransmission, the physical and MACparameters for the downstream portion being selected independently foreach customer premises equipment of the plurality of customer premisesequipment and physical and MAC parameters for the upstream portion beingselected independently for said each customer premises equipment;including the physical and MAC parameters in a control section of aframe, the control section for sending control information downstream;and allocating a first part of the upstream portion as shared and somepart of the upstream portion as unshared when there are messagesreceived but not yet acknowledged.
 2. The method of claim 1, wherein thephysical and MAC parameters are dynamically selected based on previouscommunication between the base station controller and said each customerpremises equipment.
 3. The method of claim 1, further comprising thestep of sending the control section of the frame downstream from thebase station controller to the customer premises equipment, whereby thebase station controller controls physical and MAC parameters for bothupstream and downstream retransmission.
 4. The method of claim 1,further comprising dynamically and adaptively determining new selectedphysical and MAC parameters for automatic retransmission, wherein thebase station controller determines the new selected physical and MACparameters in response to conditions of a wireless communication linkwith said each CPE.
 5. The method of claim 4, wherein the physical andMAC parameters for automatic retransmission are selected responsive to anumber of bytes successfully sent.
 6. A base station controllerconfigured to communicate with a plurality of customer premisesequipment, the base station controller comprising: a transmitterconfigured to communicate information downstream to the customerpremises equipment; a receiver configured to receive upstreaminformation communicated by the customer premises equipment; a processorconfigured to execute instructions to control the transmitter and thereceiver; and a memory storing a set of instructions, the memory beingcoupled to the processor, the set of instructions comprisinginstructions that, when executed by the processor, cause the processorto select physical and MAC parameters for automatic retransmission ofinformation between the base station controller and the customerpremises equipment, the physical and MAC parameters for downstreamretransmission being selected independently for each customer premisesequipment of the plurality of customer premises equipment, and physicaland MAC parameters for upstream retransmission being selectedindependently for said each customer premises equipment; include thephysical and MAC parameters in a control section of a frame, the controlsection being for communicating control information downstream; andallocate a first part of the upstream information as shared and somepart of the upstream information as unshared when there are messagesreceived but not yet acknowledged.
 7. The base station controlleraccording to claim 6, wherein the instructions that cause the processorto select comprise instructions that, when executed by the processor,cause the processor to select dynamically the physical and MACparameters for automatic retransmission based on previous communicationbetween the base station controller and said each customer premisesequipment.
 8. The base station controller according to claim 6, whereinthe set of instructions further comprises instructions that, whenexecuted by the processor, cause the processor to direct the transmitterto send the control section of the frame downstream from the basestation controller to the customer premises equipment, whereby the basestation controller controls the physical and MAC parameters for bothupstream and downstream retransmission.
 9. The base station controlleraccording to claim 6, wherein the set of instructions further comprisesinstructions that, when executed by the processor, cause the processorto determine dynamically and adaptively new selected physical and MACparameters for automatic retransmission, wherein the base stationcontroller determines the new selected physical and MAC parameters inresponse to conditions of a wireless communication link with said eachcustomer premises equipment.
 10. The base station controller accordingto claim 9, wherein the instructions that, when executed by theprocessor, cause the processor to select the physical and MAC parametersfor automatic retransmission cause the processor to select the physicaland MAC parameters responsive to a number of bytes successfully sentbetween the base station controller and the customer premises equipment.11. An article of manufacture comprising a memory with a set ofinstructions stored in the memory, the set of instructions comprisinginstructions that, when executed by a processor configured to causereceiver and transmitter of a base station controller to communicatewith a plurality of customer premises equipment, cause the processor toselect physical and MAC parameters for automatic retransmission ofinformation between the base station controller and the customerpremises equipment, the physical and MAC parameters for downstreamretransmission from the base station controller to the customer premisesequipment being selected independently for each customer premisesequipment of the plurality of customer premises equipment, and physicaland MAC parameters for upstream retransmission from the customerpremises equipment to the base station controller being selectedindependently for said each customer premises equipment; include thephysical and MAC parameters in a control section of a frame, the controlsection being for sending control information downstream; and allocate afirst part of upstream information as shared and some part of theupstream information as unshared when there are messages received butnot yet acknowledged.
 12. The article of manufacture according to claim11, wherein the instructions that cause the processor to select compriseinstructions that, when executed by the processor, cause the processorto select dynamically the physical and MAC parameters for automaticretransmission based on previous communication between the base stationcontroller and said each customer premises equipment.
 13. The article ofmanufacture according to claim 11, wherein the set of instructionsfurther comprises instructions that, when executed by the processor,cause the processor to direct the transmitter to send the controlsection of the frame downstream from the base station controller to thecustomer premises equipment, whereby the base station controllercontrols the physical and MAC parameters for both upstream anddownstream retransmission.
 14. The article of manufacture according toclaim 11, wherein the set of instructions further comprises instructionsthat, when executed by the processor, cause the processor to determinedynamically and adaptively new selected physical and MAC parameters forautomatic retransmission, wherein the base station controller determinesthe new selected physical and MAC parameters in response to conditionsof a wireless communication link with said each customer premisesequipment.
 15. The article of manufacture according to claim 11, whereinthe instructions that, when executed by the processor, cause theprocessor to select the physical and MAC parameters for automaticretransmission cause the processor to select the physical and MACparameters responsive to a number of bytes successfully sent between thebase station controller and the customer premises equipment.